What exactly makes Bumpkin Island the choice destination for the horde of artists who set up a makeshift colony on its shores every year? Is it the island's storied history, its grounds strewn with spooky ruins? (In addition to its past lives as a naval-training station and a fish smeltery, Bumpkin once housed a hospital for disabled children and, later, polio patients; the building burned down in 1945, but its bones are still there.) Or could it be the ridiculously scenic location, which — with its shell beaches and lush greenery — is about the closest thing to tropical paradise Boston has to offer? Then again, perhaps the goofy name was the clincher?

I never did learn the answer — turns out, the Bumpkin Island Art Encampment was pretty damn distracting, filled as it was with people building rock cairns, reading tarot cards, and attempting to summon mystical island powers with "fire-glyphs." Conceived under the partnership of the Berwick Research Institute, Mobius art gallery, and the Boston Harbor Island Alliance, the encampment project has now wrapped up its fourth year.

This go-round, seven participating artist groups (or "homesteaders") bivouacked on Bumpkin Island for a five-day residency that began on Thursday, July 29, and ended on Monday, August 2. As you might expect, a shaggy outfit like the Art Encampment isn't big on rules, but there is one: the artists must create site-specific installations that somehow improve the campground — an edict inspired by the federal Homestead Act of 1862, which granted up to 160 acres of farmland to anyone who could cultivate the soil.

In the small confines of Bumpkin Island (it takes no more than 15 minutes to walk from one end to the other), these improvements took the form of anything from a 20-foot inflatable "Montauk monster" to interpretive dance performances to an "Octopus's Garden" cobbled together from kelp, rocks, and sea urchins.

Mobius director Jed Speare described the common thread connecting Bumpkin's bizarre goings-on as "artists fulfilling self through process." He added, "At the end of our time here, there will be evidence of work, but things change, plans change." Indeed, during my Sunday trek to the island, on-the-fly improvisation ran rampant. But, as with so many acts of improv, the main drawback for Art Encampment visitors was that the art on tap seemed to be a lot more fun to make than to look at.

Luckily for those guests who took the $14 ferry trip out during the weekend's designated public-viewing days, there were plenty of opportunities to join in on the mayhem. Enterprising spectators were free to whip up their own installations — like the visitor who used bricks to spell out the words "Your Mom" in graceful cursive along one of the island's meandering trails. The cheeky sculpture served as a perfect summation of the encampment ethos: come hang out on an island and make some art if the inspiration strikes.

"The project is as much about the sun and sea as the art," said Speare, his statement reinforced by the deep-bronze tan he was sporting by Day 4. "It really gives us an opportunity to work outside the norm afforded by a gallery."